Geoscience Reference
In-Depth Information
3
4
Warm
negligible nitrate
Cool
low nitrate
1
Cold
high nitrate
2
High
Light
availability
Low
High
Nitrate
supply
Low
Figure 8.15 A schematic illustration of the changes in light availability and nitrate supply
across a tidal mixing front, and the main mechanisms supplying frontal phytoplankton
with nitrate. (1) increased vertical mixing of deep nitrate to the surface as the stratification
weakens at the front; (2) the spring-neap adjustment of the front position; (3) eddy transfer
of surface water across the front; (4) weak mixing of nitrate driven by interfacial friction
within the front.
Increases in vertical mixing at the front will only support surface productivity and
the accumulation of phytoplankton biomass as long as the rate of mixing is still low
enough for near-surface residence times of phytoplankton cells to be sufficient to
allow net growth. Figure 8.16a presents the results from a model incorporating only
this process, which show that enhanced vertical mixing alone does indeed lead to a
pattern of phytoplankton biomass within a front which is similar to observed
biomass distributions and concentrations. Allowing vertical mixing at the front to
respond to the spring-neap tidal cycle further enhances frontal production and
biomass, and leads to fortnightly pulsing of surface biomass within the adjustment
region, shown in Fig. 8.16b . This spring-neap modulation of frontal mixing has been
Search WWH ::




Custom Search